1. Technical Field
The present application relates generally to communication systems; and, more particularly, it relates to point-to-multipoint communication systems such as cable modem systems.
2. Description of Related Art
In conventional point-to-multipoint communication systems, a network supports bidirectional data communication between a central entity and multiple customer premises equipment (CPE). Example point-to-multipoint communication systems include cable modem systems, fixed wireless systems, cellular communications systems, and satellite communication systems. In each system, the communication path from the central entity to the CPE is typically referred to as the downstream, while the communication path from the CPE to the central entity is typically referred to as the upstream.
One type of point-to-multipoint system is a cable modem system, which typically includes a headend that is capable of communicating with multiple CPEs, each of which provides cable modem functionality. In a cable modem system, the CPE can be a cable modem, a settop box, or a cable gateway, to provide some examples.
DOCSIS (Data Over Cable Service Interface Specification) refers to a group of specifications published by CableLabs that define industry standards for cable headend and cable modem equipment. In part, DOCSIS sets forth requirements and objectives for various aspects of cable modem systems including operations support systems, management, data interfaces, as well as network layer, data link layer, and physical layer transport for data over cable systems. One version of the DOCSIS specification is version 2.0, and includes the DOCSIS Radio Frequency Interface (RFI) Specification SP-RFIv2.0-I03-021218 (hereinafter “DOCSIS RFI Specification”).
DOCSIS 2.0 supports the ITU-T J. 83 B (hereinafter “Annex B”) standard for downstream physical (PHY) layer transmissions from the headend to cable modems. Advances in communication technology are requiring increasingly more bandwidth, which can lead to deficiencies in channel capacity, especially with respect to these downstream transmissions. For example, even cable plants operating at a frequency of 750 MHz are being challenged with capacity shortages, due to increased demand for video on demand (VOD), high-definition television (HDTV), digital services, and expanding analog channel lineups. Numerous schemes have been proposed to help alleviate bandwidth issues, including analog spectrum reclamation and advanced video coding techniques. A DOCSIS 3.0 specification with channel bonding support has been in use for several years and a DOCSIS 3.1 proposal has been circulated.